Method for protecting a vehicle body from corrosion

ABSTRACT

A method for providing corrosion protection in an assembly of two or more metal parts follows steps of (a) at a point in an assembly process for the assembly, placing at a juncture of any two of the two or more metal parts of the assembly, a corrosion-protection element comprising heat-expandable material, the corrosion-protection element shaped to conform to the juncture; and (b) expanding the corrosion-protection element at another point in the assembly process by application of heat.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of treating boundary surfaces of avehicle body, in particular for protection against corrosion, accordingto the pre-characterizing clause of claim 1 and/or 2, as well as astructural element (corrosion-protection element) suitable for carryingout this method.

2. Discussion of the State of the Art

Protection of a vehicle body against corrosion has for centuries beenthe goal of intensive development work in vehicle construction, inparticular automobile manufacture, and has been steadily improved. Thecurrent status is so convincing that most of the large automobilemanufacturers can issue many-year guarantees against serious damage tothe body by rust.

An essential stage in the process of vehicle-body corrosionprotection—in addition to galvanizing important or all parts and ahigh-quality final lacquering—is immersion in a bath of ananti-corrosion solution, the process of cathodal electrolyticdip-priming (customarily abbreviated CDP). In this process practicallyall the sheet-metal surfaces are wetted by a highly effective layer ofmaterial that protects against corrosion, which adheres firmly to thebody when the body is removed from the bath.

Like the rest of modem automobile manufacture, the corrosion-protectionstage has now become a highly automated process, in which for reasons ofeconomy there is hardly any opportunity for manual measures to beimplemented. Nevertheless, certain regions of vehicle bodies are stillat extraordinarily great risk of corrosion, because they include weldedpoints or seams and/or are especially exposed to attack by corrosivemedia encountered while the vehicle is in use; therefore these regionsmust be treated manually to protect them from corrosion, even in thepresent state of technology.

Among these regions is the supporting structure for the MacPherson strutunit, hereinafter referred to as the MacPherson-strut dome. There iscustomarily an annular gap between a so-called outer dome and innerdome, which are welded together at multiple points to form the strutsupport. This region, embedded in the lacquering process, is manuallyprovided with an additional cover, by spraying a mass of PVC onto it orbrushing on a thick anti-corrosion layer.

This procedure is comparatively inefficient (in the overall context ofhighly automated manufacture) and involves extra costs. Furthermore,during construction of the vehicle body provisions must be made for it;that is, the region that is to be protected by this means must remainadequately accessible for manual treatment during the lacqueringprocess, i.e. even after substantial vehicle components have beeninstalled in the body.

At other places in a vehicle body, for instance in the region betweenroof bow and roof of the vehicle, or at metal edges or flanges of thedoors and the covers for engine and luggage compartments, there areregions for which an extra corrosion protection is reasonable but,according to the state of the art, can be accomplished only by manualapplication of an anti-corrosion medium. Like the corresponding measuresin the region of the strut-support dome, such corrosion-protectionoperations are associated with increased personnel effort and henceexpense. Furthermore, the relevant regions are in part visible to theeventual user of the vehicle, and the manually executedcorrosion-protection measures do not give a convincing visualimpression. In the last-mentioned region of a vehicle body, in additionto the corrosion protection it is also necessary for a lining layer tobe provided between the outer surfaces and their supports (e.g., roofand roof bow), and this at present is ordinarily produced by manualapplication of a pasty mass. This process is encumbered by the samedisadvantages as are manual corrosion-protection measures.

SUMMARY OF THE INVENTION

Hence the objective of the invention is to disclose an improved methodof protecting against corrosion and/or providing an under-lining, whichin particular is more economical and does not involve any undesirablelimitations regarding the construction of the vehicle body.

This objective is achieved (in relatively independent manifestations ofthe idea underlying the invention) by a method with the characteristicsgiven in claim 1 or 2. In addition, the invention makes available astructural element that can be employed in such a method.

The invention includes the fundamental idea of bringing about theadditional protection required for regions particularly at risk ofcorrosion by means of a prefabricated corrosion-protection element thatcan be manipulated very rapidly in a simple manner. It additionallyincludes the idea of shifting the relevant manipulation step away fromthe final-lacquering stage of production—in which the regions inquestion are in some circumstances no longer readily accessible becauseof structural considerations—into an earlier stage of the productionoperation.

Furthermore, one aspect of the first variant of the invention is thatthis step should be inserted prior to the step in which theanti-corrosion medium is applied by dip-priming. This implies provisionof a corrosion-protection element capable of surviving the relativelyhigh temperatures in the anti-corrosion bath and still firmly adheringto the associated section of the vehicle body when this processing stephas been completed. As a result of these considerations the following isproposed: in the case of a suitably shaped—in particular slot- and/orring-shaped—body region, having a structurally specifiedboundary-surface constellation such that during performance of themethod it will present sufficient resistance to an expanding structuralelement (corrosion-protection element), this region is provided, priorto immersion of the vehicle body in the bath, with a structural elementthat expands while in the CDP bath. As a result of expansion within thesaid boundary-surface constellation, the corrosion-protection elementbecomes independently “compressed” within the region to be protected. Itis securely retained there by mechanical forces after the vehicle hasleft the bath, and thus securely shields this region from externalfactors, including corrosive influences.

In the second variant of the invention, the temperatures required forexpansion by foaming of the expandable region of the proposedcorrosion-protection element are provided in a separate, thermaltreatment step. Such thermal treatment, above the foaming temperature(typically at 150° C. or more) and with a minimal duration such as isprescribed by the chemical composition of the expandable region, can berestricted to a particular region of the vehicle body. In the case ofnarrowly delimited regions, for example, it could be applied by means ofa hand-guided warming or infrared-radiation device, insofar as this canbe advantageously integrated into the technical processing sequence.

Whereas in the first variant, on account of the amount of time that mustnormally be spent in a CDP bath (15 min or more), relatively slowlyfoaming materials should be considered for the corrosion-protectionelement, for the second variant it is at present preferable to usereaction accelerators in an appropriate material, to shorten the foamingtime.

The above considerations apply equally to body regions where the goal isnot, or at least not primarily, an improved corrosion protection butrather mainly concerns the lining to be installed under these regions.With this in mind, the term “corrosion-protection element” is also usedhere to mean a lining or damping element.

In a preferred implementation of the method the corrosion-protectionelement comprises a section that expands by foaming at the elevatedtemperature and solidifies in this foamed state when it cools down. In aparticularly advantageous further development, a corrosion-protectionelement with an EVA layer that foams when heated and is disposed on athermostable carrier, in particular made of polyamide, is employed. Suchcompounds are commercially available at relatively economical prices,and simple tools can be used to shape them as required for the bodyregion to be protected.

For certain kinds of use it is also possible to employ acorrosion-protection element consisting entirely of the material capableof expansion, i.e. without a carrier.

In an application with special practical significance, to whichreference has already been made above, the region in danger of corrosionis an annular gap between an inner and an outer dome of a MacPhersonstrut support, and this region is provided with an annularcorrosion-protection element. In this application the method inparticular enables effective protection of the strut support againstcorrosion even when the construction of the vehicle is such that thisregion is entirely or partly covered by installed components during theprocessing stage in which the final lacquer coat is applied, andtherefore is no longer accessible for a manual operation.

Comparable advantages are present when the proposed method is applied inrelation to fixation elements (in particular pegs or pins) that are tobe inserted into the vehicle body. These fixation elements are set intoopenings (“bores”) in the body created for that purpose, producing anannular gap between the opening and the wall of the fixation elementthat is at risk of corrosion but can be provided with acorrosion-protection element of the kind proposed here, so that afterfoaming of said element the gap is tightly closed.

Other important applications include those in which an elongated gap,open on at least one side, between various parts of the body or adjacentsections of a single part is provided with an elongatedcorrosion-protection or lining element. The structures involved here canin particular be gaps between a roof bow and a vehicle roof, or a foldregion of a cover for engine or luggage compartment or a vehicle door,or also of a water tank associated with a vehicle body.

Here, again, extra freedom results for the constructor and technologist,who no longer needs to take care that the relevant regions are keptaccessible for manual operations even in the final lacquering stage. Inevery case the proposed method, which can be implemented to a certainextent by one manipulation, provides advantages with respect to labourcosts in comparison to the previously customary application of acorrosion-protection mass by spraying or brushing it on.

Whereas for the applications first mentioned above acorrosion-protection element is employed that has the basic shape of aring (in particular circular rings, but for special cases alsoelliptical, oval or even more complex forms, such as a FIG. 8), for thesecond group of applications a corrosion-protection element in the formof an elongated profile is suitable. In particular, this can be an I, L,T or double-T profile, or a more complex profile consisting of acombination of such standard profile shapes. The foaming section is inparticular provided in a marginal or angled region of an appropriatelyshaped carrier, or surrounds the latter. As already mentioned above, itis also possible to eliminate the carrier for special applications, sothat the profile shape is determined entirely by the thermallyexpandable material.

Altogether, then the advantages of the proposed method andcorrosion-protection element in its preferred embodiments are the time-and cost-saving elimination of manual corrosion-protection measures, theattainment of a product that makes a better visual impression byelimination of regions that appear “unclean”, an increased processingreliability by elimination of unspecified processing situationsassociated with manual interventions (unreliability of the manualcorrosion-protection operation, consumption of sealing material inamounts that are difficult to predict, variable product appeal) and, notthe least important, an improvement of environment-friendliness in thatno PVC-based substances are used for corrosion protection or as sealingand lining materials.

In an especially useful design of the corrosion-protection element,which can be reliably attached to the region of the vehicle body to beprotected and is easy to handle, in its initial state the element isprovided with one or more projections with which to fix it in the regionat risk of corrosion. Examples of such projections, which in particularare moulded extensions of a carrier (for instance, the polyamide carriermentioned above), include in particular a lip-shaped section or aplurality of small feet, which because of their shape and dimensionspossess a degree of elasticity. They are adapted to the geometry of thebody region to be protected in such a way that they can be securelyhooked or clamped there while the corrosion-protection element is in itsnon-expanded initial state.

Further advantages and useful features of the invention will be apparentfrom the subordinate claims as well as the following description of apreferred exemplary embodiment with reference to the drawings, wherein

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a sketch-like perspective representation of a MacPherson strutdome with inserted corrosion-protection element in a first embodiment,

FIGS. 2A and 2B show a partial cross section of the arrangementaccording to FIG. 1 (FIG. 2A) and a cross-sectional drawing of thecorrosion-protection element in the initial state (FIG. 2B),

FIGS. 3 and 4 are partial cross-sectional drawings of the region shownin FIG. 2A, with modified corrosion-protection elements,

FIGS. 5A and 5B show a schematic longitudinal section of a vehicle roofand a roof bow, with roof-lining means according to the state of the art(FIG. 5 a) and according to an embodiment of the invention (FIG. 5B),

FIGS. 6 and 7 are sketch-like perspective drawings of additionalstructural elements for a lining below the roof in the installedsituation according to FIG. 5B, and

FIGS. 8 and 8A to 8C are schematic cross-sectional drawings of a vehicledoor structure (FIG. 8) and of regions thereof, in which pegs are usedto anchor an external metal sheet to a door-carrier module; FIGS. 8A and8C represent one and the same connection situation at various stages ofthe assembly process.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2A show a section 1 of an automobile body that forms asupport for a MacPherson strut in the vehicle, as viewed from above in aperspective sketch (FIG. 1) and in cross section along a line A-A. Thestrut support 1 comprises an external, hood-like first sheet-metal part3, also termed outer dome, and an inner, second sheet-metal part 5, alsotermed inner dome. The outer and inner domes 3 and 5 are connected toone another by spot welds 7 arranged in a ring. Between the two domes isan annular gap 9, which in accordance with the invention is closed in amoisture-tight manner by a likewise annular corrosion-protection element11 when the element is in its final state.

The corrosion-protection element 11 is constructed as a compound with aPA66 carrier layer 13 and, firmly attached thereto, an EVA layer 15. Itis shown in FIG. 2A in its final state, after leaving a CDP bath, andshown in FIG. 2B in its initial state. At equal angular intervals itcomprises several curved processes (“small feet”) 13 a, by way of whichit resiliently overlaps an upwardly extending fold 17 of the outer dome3 and holds itself there while in the non-expanded, initial state.

Otherwise, while in the non-expanded state, the corrosion-protectionelement 11 lies within the annular gap 9 with some lateral play, so thatwhen the vehicle body is put into the CDP bath the anti-corrosion fluidcan flow past the edges of the corrosion-protection element into theannular gap so as to cover and protect the metal surfaces of the outerdome 3 and inner dome 5 here as well, in particular also in the vicinityof the welded spots 7. Within the dip bath, which typically is at atemperature of over 150° C., the EVA layer expands both laterally andinto the depths of the annular gap, as far as the metal boundarysurfaces formed by the outer dome 3 and inner dome 5. As a result, theelement is no longer fixed in place merely by the processes 13 a but isalso, over a large area, held there by the elastic pressing forceexerted by the foamed EVA layer 15, so that it seals off the annular gapin a moisture-proof manner.

FIGS. 3 and 4 show the installed situation, as seen in FIG. 2A, withmodified corrosion-protection elements 11′ and 11″. Thecorrosion-protection element 11′ shown in FIG. 3 has a carrier 13′ whichin plan view likewise has the form of a circular ring, with clampingfeet 13 a′ disposed internally and on the lower surface to fix it inposition prior to the spot welding and immersion in the CDP bath. Here,again, an expandable EVA section 15′ is moulded onto the underside, butin this case it has a triangular cross-sectional shape. An annulargroove 13 b′ on the underside of the carrier 13′ facilitates fittingonto the upward-extending section of the outer dome 3, and a sealing lip13 c′ provided at the inner edge, and bent slightly upwards, serves tocover the annular gap between inner and outer domes 3, 5 so as to give avisually perfect appearance even if certain manufacturing tolerances arepresent. Because of its flexibility, the lip 13 c′ provides a certainextra space for expansion of the EVA section 15′ as the latter foams inthe CDP bath, but simultaneously prevents the external appearance frombeing impaired by overflowing foam.

In the further modified corrosion-protection element 11″ shown in FIG.4, nearly the same carrier is used as for the structural element 11′according to FIG. 3. Therefore the identical features will not bedescribed again here. The only difference resides in the fact thatvertically extending projections 13 d″ are moulded onto the clampingfeet 13 a″ and serve to attach to the carrier 13″ a foamable section 15″that is rectangular in cross section. FIGS. 5A to 7 show, again as aschematic, sketch-like drawing, another case of application of theproposed method and structural element, involving a section of anautomobile roof 17 with underlying roof bow 19 (seen in longitudinalsection) as well as the structural elements employed here (incross-sectional or perspective representation). FIG. 5A shows howaccording to the state of the art a bead of adhesive 20 is providedbetween the roof 17 and the roof bow 19, to provide a lining between thetwo roof structures and at the same time ensure the necessary mechanicalstability. Because this dual function can lead to mechanical tensionsand deformations that might mark the outer surface of the roof, thissolution is satisfactory only under certain conditions. FIG. 5B showshow in one embodiment of the invention there is disposed between roofand roof bow a lining element 21 that comprises a thermally stablecarrier 23 and a thermally foamable section 25.

The t-stable carrier 23 can in particular consist of a polyamide, whereappropriate with fibre reinforcement and/or a proportion of recycledmaterials, and its shape is adapted to the configuration of the edgeregion of the roof bow 19 in such a way that it can be snapped orclipped onto the latter, and by virtue of its elasticity in bothmaterial and shape is reliably fixed there for the duration of theprocedure. To a section 23 a that projects from the side of the carrierprofile is attached the EVA section 25, which is approximatelyrectangular in cross section and in FIG. 5B is shown in the non-expandedstate. In the expanded state it fills up the space between the roof 17and the roof bow 19 in a flexible but moisture-proof manner, and henceboth provides additional protection against corrosion for this cavityand also serves as an under-roof lining with advantageous mechanicalproperties.

In FIGS. 6 and 7 are sketched lining elements 21′ and 21″, which aremodified with respect to the embodiment shown in FIG. 5B. The shape ofthe associated carrier, 23′ and 23″ respectively, basically resemblesthat of the carrier 23 in the embodiment according to FIG. 5B, exceptthat the lateral projection 23 a′ or 23 a″ is provided with additionalprofiling for special purposes: to accommodate two EVA strands 25.1′ and25.2′ in the case of 23 b′, or to assist retention of a flat EVA block25″ in the case of 23 b″. Another application of the invention issketched in FIG. 8 to 8C. The sketch in FIG. 8 shows a cross section ofan automobile door construction with a door-carrier module 27, an outermetal sheet 29 and a shaft reinforcement 29 a. In this arrangementplastic pegs 31, 33—the latter in combination with a threaded bolt 34(FIG. 8B)—are used to connect the door-carrier module 27 to the outersheet 29 near the upper and lower edges, respectively.

Below each of the heads 31 a and 33 a of the pegs 31 and 33,respectively, is disposed a sealing ring 35 or 37, respectively, made ofa thermally expandable material. The sealing rings are shown in theunexpanded, initial state in FIG. 8A to 8C; after they have expanded inthe course of a heat-treatment step, they produce a moisture-proof sealof the annular gap between the associated pegs 31, 33 and thearrangement provided for them (not shown separately) in the relevantbody metal. In addition, they ensure that the associated peg is kepttightly in place, and thus contribute towards preventing the occurrenceof undesired noises.

The implementation of the invention is not restricted to this examplebut is also possible in a large number of further modifications whichare within the scope of a person skilled in the art.

1. A method for providing corrosion protection in assembly of two ormore metal parts, at least one of which is made of sheet metal, andwhich are joined in a fashion leaving a space between the parts, themethod comprising the steps of: (a) forming a carrier having a groovetherein for engaging an edge region of the at least one sheet metalpart; (b) attaching to the carrier a thermally-foamable element, suchthat the thermally-foamable element, with the carrier engaging the edgeregion of the at least one sheet metal part, and the parts joined, isdisposed in the space between the parts; and (c) exposing the assemblyof the two metal parts in further processing to heat sufficient to foamthe thermally-foamable element to fill the space between the parts. 2.The method of claim 1 wherein both parts are made of sheet metal, andone has a linear edge which the groove of the carrier engages.
 3. Themethod of claim 2 wherein the parts are an automobile roof and a roofbow.
 4. A method for providing corrosion protection in assembly of ahood like sheet metal part having a circular opening with a turned-upedge, and an inner dome projecting through the opening for providing astrut support, the two parts spot-welded in a manner leaving an annulargap between the parts, the method comprising the steps of: (a) forming acarrier in a ring shape of a size to fit over the dome and cover theannular gap, and having extending processes outwardly from the ring toengage the turned-up edge of the sheet metal part; (b) attaching to thecarrier ring a thermally-foamable element, such that thethermally-foamable element, with the carrier ring engaging the turned-upedge, is disposed in the annular gap; and (c) exposing the assembly ofthe two metal parts in further processing to a heat sufficient to foamthe thermally-foamable element to fill the space between the parts. 5.The method of claim 4 wherein, in step (a) the carrier ring is formedwith an outer diameter sufficient that the carrier ring overlaps theturned-up edge, and with a groove to engage the turned up edge.
 6. Themethod of claim 4 wherein the inner dome is adapted for a Macphersonstrut.
 7. A method for anchoring a plastic peg having a shaft of onediameter and a head of a larger diameter, the peg used to join first andsecond metal parts through aligned holes in automotive assembly,comprising steps of: (a) placing a ring of thermally-foamable materialover the shaft against the head; (b) inserting the plastic peg with thethermally foamable ring through the aligned holes such that thethermally foamable ring bears against the first metal part; and (c)exposing the assembly of the peg and the two metal parts in furtherprocessing to heat sufficient to foam the thermally-foamable element toseal between the peg and the first metal part.
 8. The method of claim 7wherein the head is shaped to provided a gap between the head and thefirst metal part with the peg fully inserted, such that thethermally-foamable material when foamed, fills the gap.